Tokyo Electric Power Co. unveiled a plan that would place blocks of ice in trenches at the stricken Fukushima No. 1 nuclear power plant to help stanch the flow of radioactive water.
The method was revealed at a July 23 meeting of the Nuclear Regulation Authority. The NRA instructed TEPCO to pump out contaminated water in the trenches as early as possible because water inside the underground tunnels could be leaking into the surrounding soil.
The trenches originate at the turbine buildings and extend to the seaward side of reactors. A large volume of radioactive water, which flowed into the tunnels after the March 2011 Great East Japan Earthquake and tsunami, still has to be removed.
In late April, TEPCO began work to prevent additional water in the turbine buildings from flowing into the trenches. The utility has been constructing "ice walls" at joint sections connecting the tunnels and turbine buildings after installing bags containing cement and clay at those points.
Although the operations were scheduled to be completed at the end of May, the cement and clay bags are still not sufficiently frozen.
During the July 23 meeting, TEPCO said a small stream of water in the trenches has hampered the freezing operations. The utility said it will introduce additional freezing pipes and blocks of ice and dry ice to lower water temperatures, and also use liquid chemical agents to interrupt the water flow. The plan was approved by the NRA, but the nuclear watchdog said it will check on the efficacy of the new countermeasures as early as mid-August.
TEPCO is currently constructing a frozen soil wall around the plant’s No.1 through No. 4 reactor buildings to prevent more contaminated water from accumulating.
The delay in draining the radioactive water from the tunnels could slow the construction of the frozen wall on the seaward side of the reactors.